Tobacco smoking using a waterpipe (a.k.a., hookah) is an emerging trend and a threat to U.S. public health. Waterpipe tobacco smoke contains large amounts of toxicants (e.g., CO, tar, nicotine, and heavy metals) and has been associated with addiction and other adverse health consequences. Despite these facts, convenience sample studies demonstrate that 20-40 percent of U.S. University students report waterpipe tobacco smoking in the past year. Moreover, 30-50 percent of waterpipe tobacco smokers have never used cigarettes, suggesting that waterpipes deliver tobacco to millions of individuals who otherwise would have been naive to nicotine. Learning more about U.S. waterpipe users, mechanisms of waterpipe smoking uptake, and the trajectory and consequences of its use will be essential for developing targeted interventions to prevent waterpipe tobacco smoking from becoming a new strain in the U.S. tobacco epidemic. The American College Health Association's new National College Health Assessment (NCHA) surveys more than 90,000 individuals annually and will be the first large scale survey to include basic items that assess waterpipe tobacco smoking. This project leverages these data to help us determine the prevalence and correlates of waterpipe tobacco smoking among a large sample of U.S. university students (Specific Aim 1). Multivariable models will assess independent associations between waterpipe smoking outcomes and (1) respondent factors such as age, gender, race/ethnicity, socioeconomic status, and other substance use; and (2) environmental variables such as college/university setting, and geographic region. Next, we will use qualitative assessments to inform a theoretical framework describing the factors related to uptake of waterpipe tobacco smoking (Specific Aim 2). This component will involve (1) a national content analysis of waterpipe tobacco Web sites; (2) direct ethnographic observation of behavior in 8 different settings where waterpipe tobacco is smoked; and (3) 6 in- depth focus groups with waterpipe tobacco users stratified by age and gender. These analyses will inform our theoretical model describing the factors related to uptake of waterpipe tobacco smoking. Finally, we will conduct a nationally-representative, longitudinal study of 3700 individuals aged 15-30 investigating the trajectories and consequences of waterpipe tobacco smoking (Specific Aim 3). Data from this study will enable us (1) to test the conceptual model from Specific Aim 2; and (2) to determine longitudinal associations between waterpipe tobacco experimentation and subsequent tobacco use and intention outcomes. In sum, waterpipe tobacco smoking appears to be a growing public health threat, particularly among U.S. late adolescents and young adults. This timely and innovative project will combine analysis of an existing data set, intensive qualitative assessments, and an original longitudinal data collection to provide crucial information that will ultimately help develop interventions aimed at reducing the public health threat posed by waterpipe tobacco smoking.